"A financial institution is not allowed to inform a business or consumer that a SAR is being filed, and all the reports mandated by the BSA are exempt from disclosure under the Freedom of Information Act."
Roughly, if you deposit more than 10K USD in cash, they will need to file this form with the OCC. And, a bunch of other activities qualify. There is no guarantee that this will result in account closure, not does it directly indicate illegal activity. This seems to be a myth online. In the industry, the SAR is regarded as a "get of jail free card" for poorly staffed compliance departments. "When in doubt, file a SAR!", then the bank cannot be so easily sanctioned for allowing illicit activities.
"A financial institution is not allowed to inform a business or consumer that a SAR is being filed, and all the reports mandated by the BSA are exempt from disclosure under the Freedom of Information Act."
(not speaking on behalf of my employer)